I would remove the iac valve and clean it thoroughly with carb cleaner,if its a two piece unit disassemble it and clean the mechanical part of it.Twist the pintle and push it back and forth to make sure its not sticking,dry it with an air compressor,reassemble then reinstall.If gasket tears,replace it or at least use rtv so you won't create a vacuum leak.If that doesn't help,check for vacuum leaks.Let engine idle,spray carb cleaner on every gasket,vacuum hose,and vacuum operated component.If the engine suddenly idles up or stalls,you have found the leak.If that doesn't locate the problem,suspect the tps sensor as a possible cause.You can test it with a voltmeter.Probe the signal and ground wires with key on.Voltage should be 0.45-1.10 volts.Now open the throttle slowly and watch meter.Voltage should range from 1.0-5.0 volts with no erratic movement or voltage spikes.If it fails either test,the tps is defective.Inspect the throttle cable too making sure it isn't sticking.

#1. Replace the fuel filter first.

#2. Take the SUV to a Chevrolet Dealer and ask then to test the fuel pressure on the fuel rail pressure fitting. This is a very inexpensive test BUT the fuel filter must be clean to get an accurate fuel pressure reading.

The wandering idle problem could be caused by the idle speed solenoid inside the front of the throttle body.

Vacuum leak comes to mind and cleaning the throttle body and air by pass would be next.

Mass airflow sensor.

why is my 04 trailblazer running at about 500 rpms or lower when coming to a stop sign or red light and bucks like its out of gas sometimes stalling but when i shut it off and turn bk on its fine also as soon as I hit the gas a little bit it will accelerate byitself and I put it in neutral and the rpms shoot very high forcing me to shut it off. also it smells like really rich gas or kinda like starting fluid some side effects is it louder when taking off also its very hard to get up to speed with no balls until I reach about 4 rpms then it will take off like a bat outta hell. also while using the cruise on the high way it will act like u just turned the cruise control off and start loosing speed then my rpms jack way up to about 4000 and then will smooth back out and go bk to the speed it was set at. ive cleaned the throttle body multiple times and still doing the same thing but when I unhook the battery my engine light goes off its quite again a runs great for about 30 minutes then does the same ****. any ideas im short on cash so I cant replace every option but will replace what a majority of you thionk it may be